In a biomedical laboratory, usually a volumetric pipette is adopted to quantitatively sample and transfer the liquid specimens. However, in order to avoid cross-contamination among the specimens, the volumetric pipette is capped with a disposable sampling head (as so-called “tip”). Basically, the sampling head can be used only for one time. A principle of the volumetric pipette in operation is that the specimen enters into the sampling head by vacuum method; and likewise, the specimen is outlet from the sampling head by a thrust force generated by the vacuum method. Generally, a main body of the sampling head is shaped cylindrical with converging to a tapered opening at its bottom.
A liquid specimen sampled for a biomedical laboratory includes, for example, a serum, plasma and whole blood, which contains a large amount of protein, carbohydrate, fat, blood cell, cell, and microorganism such that the liquid specimen belongs to a viscous liquid which contains particles and/or colloid substances. Therefore, a manner of operating the tapered opening of the sampling head on an accurately-and-correctly quantitative sampling exists a certain level of difficulty. In manual operation, the operator can avoid “clog” from the particles and/or colloid substances by instant human-eye observation on inspecting whether a volume of the suctioned/discharged specimen is correct or not, or can immediately stop suction/discharge to avoid contaminating the volumetric pipette when the “clog” occurs.
Basically, the accuracy and correctness of specimen suction/discharge are very important. If the correctness of the specimen suction/discharge could not be ensured, this might invoke false negatives or false positives, thereby resulting in misjudgment of the experimental results.
In the conventional art, the automated equipment has several following problems that include: 1. liquid level detection; 2. clog detection; and 3. volume detection.
For the liquid level detection, the volumetric pipette is able to detect the liquid level of the specimen for suction/discharge depending on the position of the liquid surface. This can prevent the sampling head from entering under the liquid surface of the specimen, and to dip too much of the specimen to generate carry-over and cross contamination matters.
For the clog detection, in the manner that the volumetric pipette could not be detected in time but continue to suction when the tapered opening of the sampling head is blocked, it will cause the internal pressure of the sampling head to be abnormal. When a clogging is suctioned into the sampling head, the specimen may be ejected into the inside of the volumetric pipette due to the pressure, thereby contaminating the volumetric pipette and thereby affecting subsequent sampling.
For volume detection, the suctioned specimen needs to be fixed whereby it is important to detect the volume of each sampled specimen, especially for use in the automated equipment.
However, in the automated equipment, it is urgent to solve the above three technical issues, and to ensure the accuracy and correctness of the specimen suction/discharge without the operator's inspection.
With reference to U.S. Pat. No. 5,648,727, which places a capacitive sensing element on a volumetric pipette in conjunction with an electrically conductive pick-up head, so that when the conductible head is close to the liquid level of the conductible specimen, a current is generated dependent upon the capacitance difference, and then the height of the liquid level is acquired based on calculating the current. However, this method has a problem of detecting errors for a non-conductive specimen or a foamed specimen.
With reference to U.S. Pat. No. 8,287,806, which provides a sensor for detecting a pressure difference, the air inside the suction head is compressed to produce a pressure change when the specimen enters into the suction head. Furthermore, a volume of the specimen within the suction head can be acquired by calculating the pressure difference. However, this method requires a complete air-tightness, which also means a higher cost required. At the same time, once if there is any air leakage, error measurement is inevitable.
With reference to U.S. Pat. No. 8,100,007, the method of this patent includes the steps of: first, to detect the level of the liquid surface of the specimen and then to lower the suction head to the liquid surface of the specimen when the liquid level of the specimen is detected, to absorb the specimen. There is a drawback in that the determination of the volume of the suctioned specimen and the clog judgment could not be simultaneously performed during the suctioning process of the specimen. For the automated equipment, such a drawback would result in several technical problems of contamination of the quantitative pipette and/or other contaminations.
However, the conventional art provides solutions to the above-mentioned technical problems, but there is no effective way to solve the above-mentioned technical problems at the same time.